What seemed to be a relatively peaceful second night of protests near St. Louis suddenly turned violent late Saturday when a small group of demonstrators refused to disperse, police said.

The demonstrators were reacting to Friday’s acquittal of a white former St. Louis police officer who stood trial in the 2011 shooting death of a black suspect.

Saturday’s confrontation took place in the Delmar Loop of the St. Louis suburb of University City — known for concert venues, restaurants, shops and bars. The area had been the scene of a peaceful march earlier in the evening that ended with organizers calling for people to leave and reconvene Sunday afternoon.

But the small group that stayed behind drew hundreds of police in riot gear, who moved in and ordered them to leave. The demonstrators retreated down a street, breaking windows and throwing objects at police.

Some protesters were seen in handcuffs but the number of arrests was not immediately known.

Earlier Saturday, demonstrations consisted mostly of marching and chanting through University City in a change from Friday evening’s violence, which saw 11 police officers injured – several by bricks tossed from the crowd – and the smashing of windows at the home of Mayor Lyda Krewson.

Krewson wasn’t home at the time, but family members were. She called the vandalism “irritating.”

“These are not the images we want to see of our city,” Krewson said at a news conference Saturday, the St. Louis Post-Dispatch reported. “We have some work to do here.”

The protests were sparked by Friday’s acquittal of former St. Louis police Officer Jason Stockley, 36, who stood trial for first-degree murder in the December 2011 shooting death of suspect Anthony Lamar Smith.

The trial came in the wake of the August 2014 shooting death of Michael Brown in nearby Ferguson, Mo., another police-involved death that sparked days of unrest in that town and elsewhere. The white officer in that case did not face charges.

Friday’s violence in St. Louis prompted the cancellation of concerts planned by rock band U2 on Saturday and singer Ed Sheeran on Sunday. Other events were postponed or canceled as well, the St. Louis Post-Dispatch reported.

Earlier Friday, FOX2 in St. Louis captured video of an elderly woman being knocked down and trampled by riot police. That woman, who was unidentified, was charged with “interfering,” St. Louis police tweeted Saturday.

On Saturday, U2 frontman Bono issued a statement on Instagram about the cancellation and about the events transpiring in St. Louis, Variety reported.

“Deeply saddened at what has happened in St. Louis and having to cancel our show tonight,” Bono’s statement read. “I found myself reading Dr. King’s speech from the National Cathedral and asking myself is this 1968 or 2017?”

St. Louis police said 33 people were arrested in connection with Friday’s protests. In addition to the mayor’s home, there was also damage to two police vehicles, the St. Louis Public Library and 10 businesses in the city’s Central West End, police said.